For example, as disclosed in Japanese Utility Model Unexamined Publication No. Hei 1-174625 and Japanese Patent Examined Publication No. 57-38812, a ball bearing for rectilinear sliding shown in FIG. 1 is conventional.
These conventional art ball bearings include a raceway track base 51 having ball rolling grooves 50 on the upper and lower portions of both sides thereof and a slide guide member, wherein wing portions 54 are formed at the both sides of a horizontal portion 53 extending downwardly in a perpendicular direction so as to form a concave portion 55 by the horizontal portion 53 and the wing portions 54. Load ball grooves 56 are provided at upper and lower portions on the inside surface of the respective wing portions 54, and no-load ball raceway tracks 57 are provided, corresponding to the load ball grooves 56, through the respective wing portions 54 so as to form a slide member 58. Plastic caps (not illustrated) having respective return grooves, corresponding to the load ball grooves 56 and the no-load ball raceway tracks 57, at right and left portions thereof are provided at the front and rear end surfaces of the slide member 58, so that four endless ball (hereinafter referred to as "ball endless") circulation passages are formed by the load ball grooves 56, the ball rolling grooves 50, no-load ball raceway tracks 57 and the return grooves. A ball retainer 60 having ball projecting windows 59 shown in FIG. 2 is fixed on the concave portion 55 formed by the horizontal portion 53 and both wing portions 54. Balls 52 are placed into the ball endless circulation passages, and the balls 52 are retained by the ball retainer 60. The slide guide member which comprises slide member 58 with balls 52 and ball retainer 60 is fitted onto the raceway track base 51, and as a result, the slide guide member is provided slidably relative to the raceway track base 51.
Since these conventional structures shown in FIG. 1 and 2 have the above-described structure, they have a disadvantage in that it is very difficult to place the balls 52 into the ball endless circulation passages.
To describe the placing work for balls 52 concretely, firstly, a cap having return grooves is fixed to one end surface of the slide member 58. Secondly, the ball retainer 60 shown in FIG. 2 is fixed on the inside surface of the slide member 58, the balls 52 are inserted, being supported by the slide member 58, one by one into the gaps, formed by the ball retainer 60 and the load ball groove 56, and into the no-load ball raceway tracks 57. After the predetermined number of balls 52 have been inserted, finally, another cap is fixed to another end surface of the slide member 58.
However, since the balls 52 are inserted into the gaps formed by the load ball groove 56 and the ball retainer 60 and the no-load ball raceway track 57, which are approximately equivalent in diameter with the balls 52, the balls 52 cannot be inserted adequately into the gaps and the no-load ball raceway tracks 57 and such placement is very difficult.
Moreover, since the predetermined number of the balls 52 must be placed into the ball endless circulation passages, when the cap is fixed to another end surface of the slide member 58 at last, grease is applied in the return grooves of the cap, and several balls 52 are attached to the grease so that the predetermined number of the balls are placed into the ball endless circulation passages. Subsequently, the cap is fixed to another end surface of the slide member 58 so that the balls 52 are prevented from fallingout. Even, under this condition, i.e., in the conventional manner, it is difficult to place balls into the ball endless circulation passages and to automate such a process.